The present invention relates generally to telephone networks, and more particularly to an interface between fiber optic transport media and a switching system designed for electrical signals.
As multimedia applications increase the demand for high-bandwidth, high-bit-rate communications, fiber optics technology is rapidly advancing to supply the capacity. A family of standards for optical fiber transmissions is known as the Synchronous Optical Network (SONET) standards. SONET was born as an extension to the DS1 hierarchy, which is a hierarchy of xe2x80x9celectricalxe2x80x9d as opposed to xe2x80x9copticalxe2x80x9d signals and consists of levels of signals formed by multiplexing lower level TDM (time division multiplex) signals.
The SONET standard establishes a multiplexing format for using any number of 51.84 Mbits/s signals as building blocks. An OC-3 (Optical Carrier, Level 3) is a 155.52 Mbits/s signal (3xc3x9751.84 Mbits/s), and its electrical signal counterpart is referred to as an STS-3 signal. The STS-1 signal carries a DS3 signal or a number of DS1 or other lower level signals. A SONET STS-3 signal is created by concatenating STS-1 signals. Each SONET STS-N electrical signal has a corresponding OC-N xe2x80x9coptical signalxe2x80x9d. The OC-N signals are created by converting the STS-N electrical signal to an optical signal.
Although optical switching techniques have been developed, telecom companies are eager to provide as much performance as possible from their existing infrastructure. Switching systems based on the DS1 electrical signal hierarchy are in place and continue to be used for signals carrying that type of signal. Essentially these switching systems use DS0 data, which is derived from the DS1 hierarchy. For example, a DS1 signal is comprised of 24 multiplexed DS0 voice channels. Thus, there is a demand for interfaces that will permit SONET signals to be switched through switching systems designed for the DS1 hierarchy of signals.
One aspect of the invention is a method of transporting data in a delivery unit that interfaces telecommunications media that carries network data to a switching system that switches network data channels. The primary transport is performed by transporting network data between application modules of said delivery unit by means of ingress and egress buses to and from a bus control module, said ingress and egress buses carrying both control data and network data. However, an alternate transport means is also available for control data, and is accomplished by the following steps: originating a control message at a unit controller module of the delivery unit; establishing a maintenance communications link between the unit controller module and the bus control module that is separate from the ingress and egress buses, and delivering the control message to said bus control module via this maintenance communications link.
An advantage of the invention is that if there is a failure in the transport paths to the bus control module, it may nevertheless receive control messages. It can be reset or receive other messages for handling fault detection and recovery.